Sommerstein spent most of his life in Lwów, where in the interwar period he was director of the Lawyers Office. Between 1922 and 1939, he was a deputy to the Polish Parliament (with a break from 1927 to 1929), where he was a member of several commissions. He also published articles in several Polish and Jewish newspapers and magazines, such as Chwila, Glos Prawa and Gazeta Bankowa.
Among others, he founded first organization of Jewish farmers - Lesser Poland's Union of Farmers, and in 1933, he co-created United Antihitlerite Committee in Warsaw. When Lwow was annexed by the Soviet Union in its invasion of Poland, Sommerstein organized the Committee of Helping Jewish Refugees from Germany. Arrested by the NKVD, he was sent to a Gulag prison camp, and later released. After the war, he was released on the condition that he become the Minister for Jewish Affairs in the communist-sponsored Polish Committee of National Liberation provisional government. He used this position to help Armia Krajowa partisans flee to the United Kingdom in disguise as Orthodox Jews.[2] In 1946 Sommerstein left Poland for USA, where he died.
